chore: improve status-update workflow and document auth stabilization
Updates the /status-update slash command with a structured workflow:
1. Read current STATUS.md state
2. Find undocumented work via git history
3. Understand WHY changes were made (not just what)
4. Write contextual documentation for future readers
Documents recent auth stabilization work (PRs #734-736):
- Session expiry now respects refresh token lifetime
- Queue component uses shared auth state (SSR boundary fix)
- BytesIO accepted in R2Storage.save() (playlist cover fix)
🤖 Generated with [Claude Code](https://claude.com/claude-code)
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>